Plagiostomidae is a family of marine, free-living flatworms in the order Prolecithophora.
Species of Plagiostomidae have an oblong body with the mouth at the anterior end and the gonopore near or at the posterior end. They typically have one or two pairs of eyes and lack a brain capsule and a ciliated groove around the anterior end of the body.
Nine genera are currently considered in Plagiostomidae. However, at least one genus, Plagiostomum, is paraphyletic.